Control systems have been developed for monitoring and automatically controlling the operation of various types of construction equipment, such as for example excavators. Such systems of this general type are disclosed in U.S. Pat. No. 5,461,803, issued Oct. 31, 1995, to Rocke; U.S. Pat. No. 5,062,264, issued Nov. 5, 1991, to Frenette et al; and U.S. Pat. No. 6,447,240, issued Sep. 10, 2002, to Cain et al. In each of these patents, a positioning and control system is disclosed that includes an arrangement for measuring the relative positions of various machine elements.
While it is desirable to be able to determine the relative positions of machine components, it is also useful to be able to monitor the position of a machine at a construction worksite. Global positioning systems, laser systems, and ranging radio systems have been developed and combined to accomplish this goal. One such system is shown in U.S. Pub. No. US 2008/0247758, to Nichols, published Oct. 9, 2008. The Nichols published application discloses various combinations of GPS, laser, and ranging radio receivers that are carried on a mobile user unit.
Ranging radios offer an excellent alternative to GPS receivers for positioning applications where GPS reception is not available or use of GPS receivers is not desired. For example, GPS receivers require line of sight access to multiple satellites in order to function properly. This may not be possible in some operational settings, such as when work is being performed indoors, underground, or in cluttered environments. For example, when an excavator is operated in a strip mine, it may work adjacent a mine wall that effectively blocks out some or all of the satellite transmissions that are needed for proper GPS function. As another example, an excavator may be operated in mountainous or heavily forested areas, and GPS operation may be impractical.
Ranging radios, operating at ultra wideband (UWB) frequencies, provide very accurate measurement of distances between radios using time of flight analysis. To perform a range measurement, an originating ranging radio transmits a packet consisting of a synchronization preamble and a header. The header contains the range command with the address of the destination radio which is requested to respond to the packet. The originating radio resets its main counter at the time of this transmission, establishing a local time-zero reference. When the destination ranging radio receives the range request addressed to it, it records the time of receipt, and replies with its own packet, including the time of receipt and the time of the responding transmission in the header. The originating radio receives the ranging packet back from the destination radio, records its time of receipt and latches its main counter. The range value is then calculated and recorded, utilizing the time information to compensate for the differences in the timing clocks at the two radios.
It is desirable to provide an improved system using ranging radios in which the positions of the operating elements of an excavator or other machine can be determined and controlled.